The present invention relates to a wavelength converting device, and more particularly to a wavelength converting device which includes a light waveguide made of nonlinear material and generates SHG light or sum and difference frequency light.
There has been known a wavelength converting device in which Cherenkov radiation light is produced from a light waveguide formed on a LiNbO.sub.3 crystal by a proton exchange method.
In this device, second harmonic generation (SHG) light in the form of Cherenkov radiation can be obtained with a converting efficiency of 1% when a semiconductor laser beam is incident on the light waveguide.
The wavelength converting device with a similar light waveguide can produce sum and difference (sum/difference) frequency light in the form of Cherenkov radiation. For example, it is known that from two incident light beams having wavelengths of .lambda..sub.1 of 1.06 .mu.m and .lambda..sub.2 of 0.824 .mu.m, the device produces sum frequency light having wavelength .lambda..sub.3 of 0.463 .mu.m, where 1/.lambda..sub.1 +1/.lambda..sub.2 =1/.lambda..sub.3.
In such wavelength converting devices, much of the light introduced into the light waveguide is output with the wavelength remaining unconverted, so that the conversion efficiency is low.
To improve the conversion efficiency, it is necessary to elongate an optical path of the light waveguide. However, this leads to an elongation of the device itself, making the device bulky.
Further, in the above wavelength converting devices, the output light is obtained only in one direction, and not obtained in the other directions.
Furthermore, in the sum/difference frequency generating device, a wave combining means such as a dichroic mirror must be provided prior to the light waveguide in order to introduce two input light beams of wavelengths .lambda..sub.1 and .lambda..sub.2, since the light waveguide is rectilinear in shape. In the case where two light beams of .lambda..sub.1 and .lambda..sub.2 are led through optical fibers to the device, the light beams emanating from the optical fibers are first collimated by objectives, the collimated light beams are combined and then converged by an objective, and are finally led to the light waveguide. Practically, it is very difficult to make the optical axis of the .lambda..sub.1 light coincident with that of the .lambda..sub.2 light. Further, the device becomes complicated and bulky.